Harbaugh also said that Crabtree is not expected to miss the entire 2013 season, though he declined to give a timetable for Crabtree's return.

The injury happened Tuesday during a 7-on-7 drill at organized team activities. Crabtree suffered a complete tear of his Achilles.

"He was coming in motion and just was planted and started a route and felt like somebody kicked him in the Achilles, which sometimes people say that feels like," Harbaugh said. "The good news is, he woke up from the surgery and the first thing he asked the doc was how it went."

San Francisco 49ers' Michael Crabtree (15) breaks loose on a pass play against the Atlanta Falcons for a first down in the fourth quarter of the NFC Championship game on Sunday, Jan. 20, 2013 at the Georgia Dome in Atlanta. (Jim Gensheimer/Bay Area News Group)
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Jim Gensheimer
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When told by the doctor who performed the surgery at Stanford that the surgery went well and that he likely won't miss the whole season, Crabtree showed the kind of positive approach Harbaugh expected.

"His comment to that was, he's got no choice but to be back," Harbaugh said. "Every day now is a healing day, and that starts today."

Losing Crabtree would be a significant blow to the reigning NFC champions and Colin Kaepernick, who's entering his first full season as the starting quarterback.

Crabtree was expected to remain the 49ers' No. 1 receiver and be complemented by veteran Anquan Boldin, who was acquired in a March trade with the Baltimore Ravens.

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Now, Kaepernick and Harbaugh said, it's time for someone other than Crabtree to assert himself.

"We have a lot of talent out here," Kaepernick said. "It's just: Who's going to step up and fill that role?"

The 49ers 'top backup receivers, Mario Manningham and Kyle Williams, are both coming off late season knee injuries, each player having torn an anterior cruciate ligament.

A.J. Jenkins, last season's first-round draft pick who didn't produce a single reception, has added muscle this offseason in an attempt to crack the lineup.

Another intriguing receiver is Ricardo Lockette, a 6-foot-2 speedster who is Kaepernick's roommate and has worked out all offseason with the blossoming quarterback.

Other options at receiver are Marlon Moore, Joe Hastings, Chad Hall and Quinton Patton, a fourth-round draft pick who signed a four-year contract Wednesday.

"We're excited for the young receivers that we have," Harbaugh said. "I really feel that somebody is going to emerge there, because they have to. Competition will create that, and we'll look forward to watching that."

Randy Moss, who started all three playoff games, is a free agent and wasn't expected to return, at least before Crabtree's status changed.

Harbaugh refused to speculate about re-signing Moss. He said he won't comment on players not on his roster.

Crabtree's breakout season last year continued at a fever pitch once Kaepernick replaced Alex Smith as the 49ers starter over their final 10 games. Never was that more evident than the end of the 49ers' Super Bowl defeat, when Kaepernick unsuccessfully targeted Crabtree on his final three passes from the Baltimore Ravens' 5-yard line.

Crabtree had five receptions for 109 yards and a touchdown in that 34-31 Super Bowl defeat. He opened the playoffs with a nine-catch, 119-yard, two-touchdown showing against the Green Bay Packers.

Crabtree had a six-catch, 57-yard output in the NFC Championship win at Atlanta, doing so while San Francisco police investigated a sexual-assault allegation against him (to which charges were never filed).

Crabtree's career has been a tumultuous one aside from last season. A contract stalemate kept him out of the first five games of the 2009 season. Foot injuries had hampered his availability his first few years, and he didn't appear in an exhibition game until last year.

Crabtree proved especially prolific on third downs, tying for the league's fourth-most with 30 such receptions last season.